Method and device for stacking flat items of mail in a stack holder

ABSTRACT

According to the invention, the items to be posted are held by a stacking support which can be displaced in a stacking direction and is coupled to a flush-mounted strip on which the stack is arranged, and by a parallel stacking wall which is located in a vertical position on the stacking spot, oriented towards an abutment wall. Said items to be posted are supplied and stacked by means of stacking belts and a stacking roll which projects from the stacking wall and is located at the entrance to the stack receiving installation, close to the abutment wall, said stacking roll being mounted in a deflectable manner. A connecting element is used to connect the stacking roll housing to the force transducer of a device for measuring the stacking pressure perpendicularly to the resulting belt force exerted on the stacking roll.

The invention relates to a method and a device for stacking flat items of mail in a stack holder according to the preambles of claims 1 and 6.

The items of mail of different formats should all be aligned exactly on two edges.

For each item of mail to be stacked, the force of the stack against the stacking roller (stacking pressure) must be adjusted optimally, so that each item of mail reaches the stop wall and its leading edge and bottom edge are aligned exactly flush with the items of mail already stacked. The actuating variable for the control of the stacking pressure on the stacking roller is the forward thrust of the movable stack support, to which an underfloor belt can also be coupled.

As a result of stacking an item of mail, the stacking pressure increases and can be reduced again and set optimally by moving the stack away from the stacking roller or by advancing the underfloor belt with the stack support. In order to control the stacking pressure, it is necessary to measure the latter.

According to the prior art, there are one or more force measuring devices on the stacking wall in the region lying around the stacking roller. For example, in DE 195 47 292 A1, an intermediate stacker is described in which, for the purpose of stacking pressure measurement, one or more sprung levers, against which the stack of items of mail presses, are arranged in the vicinity of the stacking roller. The levers actuate switches which output switching signals for the drive of the stack support with the underfloor belt. As soon as a specific minimum pressure acts on the lever or levers, a signal to move the underfloor belt and the stack support away from the stacking roll is triggered. If the pressure falls below a specific minimum, the underfloor belt with the stack support remains in the position then assumed.

For the optimum stacking of an item of mail, the force between the stack and the stacking roller (“stacking force”) is primarily critical, because the level of the friction between the item of mail and the stacking roller (or the stacking belt) depends directly on this and because the force effecting the transport of the item of mail is exerted on the item of mail via the stacking roller (or the stacking belt).

However, the previously disclosed solution permits only a measurement of the pressure between the stack and one or more contact points of the stack (lever) on the stacking wall in the region around the stacking roller (that is to say on the force measuring devices, which represent only a force shunt in relation to the functionally relevant force flow via the stacking roller). Thus, direct measurement of the stacking pressure is not possible, only a rough estimate of the stacking pressure via the measured force shunt.

The invention is therefore based on the object of providing a method and a device for stacking flat objects in which the stacking pressure to be controlled is measured more accurately.

According to the invention, the object is achieved by the features of claims 1 and 6.

The stacking pressure is measured directly on the stacking roller approximately perpendicular to the direction of the resultant belt force acting on the stacking roller, via a deflection of the stacking roller. For this purpose, the deflectable stacking roller mounting is connected via a connecting element for force transmission to the force sensor of the force measuring device in order to measure the stacking pressure perpendicular to the resultant belt force.

As a result, there is no distortion of the stacking pressure acting on the stacking roller resulting from force shunts.

Because the stacking roller has to absorb the resultant belt force in addition to the stacking pressure, the relatively small stacking pressure has to be separated from the large resultant belt force, which is not constant and otherwise would distort the measured result. This is done in that, from the stacking force, only the part which is approximately perpendicular to the resultant belt force is measured, so that the force directions are decoupled vectorially.

Advantageous refinements of the invention are presented in the subclaims.

Thus, it is advantageous to provide a bending beam with strain gages as the force sensor in the force measuring devices, and the deformation approximately perpendicular to the resultant belt force serving as a measure of the stacking pressure. In this measuring principle, disruptive forces arising from measuring-travel-induced displacements of the force direction are largely avoided with the minimum measuring travel.

It is also advantageous if the stacking roller is deflected only approximately perpendicular to the direction of the resultant belt force.

In order to compensate for any geometric inaccuracies and the stresses resulting from this and not to transmit any transverse forces to the force measuring device, the transmission of force from the stacking roller to the bending beam of the force measuring device is advantageously carried out via a connecting element which is designed to be stiff in the force transmission direction approximately perpendicular to the resultant belt force and compliant at right angles thereto.

It is also advantageous to fit the force measuring device to a carriage such that it can be adjusted, in order to compensate for mounting-induced or tolerance-induced prestresses.

The deflection of the stacking roller is advantageously achieved by the stacking roller bearing being fixed to a movable swinging arm.

In order that the direction of the resultant belt force is not changed by the stacking belt lifting off a deflection roller for the other stacking belt, located upstream of the stacking roller in the transport direction, as a result of an item of mail, which briefly produces disruptive forces, it is advantageous to carry out the measurement of the stacking pressure when there is as yet no following item of mail between stacking belt and deflection roller. If this is not possible, then the changed direction of the resultant belt force as a function of the thickness of the following item of mail can be taken into account by computation during the force measurement.

The invention will be explained in more detail below in an exemplary embodiment, using the drawing, in which:

FIG. 1 shows a plan view of the stacking device;

FIG. 2 shows a perspective illustration of the stacking roller with force measuring device, obliquely from below;

FIG. 3 shows a perspective illustration of the stacking roller with force measuring device, obliquely from above.

As FIG. 1 reveals, the items of mail are transported one after another in the direction of the stacking roller 4 in an upright position and clamped between stacking belts 1, 2. In order that the stacking can be carried out, the stacking belt 2 oriented toward the stack upstream of the stacking device is deflected over a deflection roller 3, whereas the other stacking belt 1 is only deflected over the stacking roller 4. Because of their kinetic energy and as a result of frictional forces, the items of mail are led at an acute angle α along the stacking belt 1 to the stacking roller 4 onto the stack support 11 located there, if no item of mail has yet been stacked, or against the item of mail last stacked on the stack, and are then held between the stack support 11 and a stacking wall 7 which is parallel thereto and from which the stacking roller 4 protrudes somewhat. The stacking pressure which prevails between the uppermost item of mail of the stack and the stacking roller 4 must in this case be sufficiently high for each item of mail to pass securely between the stacking roller 4 and the stack support 11 or the uppermost item of mail of the stack until it strikes the stop wall 8, on which the kinetic energy of the item of mail is dissipated. In order that the stacking pressure does not become too high following the stacking of an item of mail, the stack support 11 and the stack base in the form of an underfloor belt 9 must be moved away from the stacking point.

This is done by the driven underfloor belt 9 and the stack support 11 coupled to the latter being moved appropriately via a control device, not illustrated, as a function of the measured stacking pressure. The coupling is carried out by slot-like cutouts 12 in the underfloor belt 9 and the stack support 11 shaped in such a way that it can be anchored in one of the cutouts 12. Since the stack support 9 can be pivoted upward on an axle 10 located in the stop wall 8, the stack can be pushed out during unloading after the stack support 11 has been pivoted up. The stack support 11 is then pushed back on the axle 10 as far as the stacking roller 4 and pivoted down again and anchored in the appropriate cutout 12 in the underfloor belt 9. A new stacking cycle then takes place. The stacking pressure measurement is carried out directly on the deflectable stacking roller 4. Since the higher resultant belt force F_(R) also acts on the stacking roller 4, the stacking pressure F_(S), which is small in relation thereto, must be decoupled from the belt force F_(R) on the stacking roller 4. This is done in that, of the stacking pressure F_(S), only the component F_(SS) approximately perpendicular to the direction of the resultant belt force F_(R) is measured. Thus, the two force directions are vectorially independent of each other.

In order to ensure this, the stacking roller 4 is mounted such that a minimum deflection approximately perpendicular to the resultant of the belt force F_(R) (that is to say in the direction of F_(SS)) can take place with minimum force. For this purpose, the stacking roller 4 is mounted on a movable swinging arm 14 such that it can be pivoted with minimum friction. Mounting the stacking roller 4 on an element which can be deformed easily in this direction is in principle also possible. In the direction of the possible deflection, the measurement of the force component F_(SS) is carried out by a force measuring device, which is connected to the swinging arm 14 of the stacking roller 4 by a form fit.

The force component F_(SS) is transmitted to the force measuring device by a connecting element 5, which is designed to be particularly compliant about the two axes perpendicular to the force measuring direction, in order to compensate for any geometric inaccuracies and the stresses resulting therefrom and not to transmit any transverse forces to the force measuring device. The connecting element 5 is designed to be as stiff as possible in the force transmission direction. For the purpose of force measurement, use is made of a measuring principle having minimum measurement travel, for example by means of bending beams 6 with strain gages, in order to minimize disturbing forces resulting from the displacement of the force measuring device caused by the measurement travel. The connecting element 5, as can be seen well in FIGS. 2 and 3, is fixed by screw connections to the bending beam 6 and to a fixing element of the rotatably mounted swinging arm 14. On the swinging arm 14 there is also the mounting 13 of the stacking roller 4.

In order to compensate for mounting-induced and tolerance-induced prestresses of the force measuring device in the measuring direction, the bending beam 6 is fixed to a carriage 15 which can be adjusted in the measuring direction and fixed.

Depending on the magnitude of the angle β between the resultant belt force F_(R) and the stacking wall 7, the force component F_(SS) changes. Given an angle β of approximately ≧30°, it is still sufficiently large to achieve meaningful measured results. If the force measuring device is arranged more in the direction of the stacking pressure F_(S) to be measured rather than in the movement direction of the stacking roller 4, cos β tends to 1, and thus F_(SS) tends to F_(S). However, the direction of movement of the stacking roller 4 no longer coincides with the force measuring direction at minimum deflection, which means that, as the measurement travel increases, stresses and disturbing forces can be produced. These can be compensated for by the most part by the connecting element 5. Nevertheless, the force measurement will be carried out approximately in the direction of movement of the stacking roller 4, since in this case the vectorial separation of F_(R) and F_(S) is reliably ensured and, for example, fluctuations in the resultant belt force F_(R) arising from different belt tension cause virtually no disturbing forces in the force measuring direction.

It is advantageous to carry out the measurement of the stacking pressure F_(S) at a time at which there is no following item of mail between stacking belt 1 and the deflection roller 3, since the direction of the resultant belt force F_(R) is easily affected as a result of the stacking belt 1 lifting off the deflection roller 3 (depending on the thickness of the following item of mail), and thus for a short time disturbance forces act on the force measuring device.

In order to be able to change the stacking belt 1 without great effort and without any tools, the swinging arm 14 is fitted underneath the stacking roller 4 (between stacking roller and letter running plate), in order not to block the stacking belt 1 in.

In order that the stacking wall 7 does not have to be dismantled during a belt change, it is provided with a door which can be folded and which permits the stacking belt 1 to be removed upward. 

1. A method for stacking flat items of mail in a stack holder, the stack holder comprising a stack support, stacking point, stacking wall arranged parallel to the stacking point, stop wall, and an underfloor belt on which the stack stands, comprising the steps of: holding the mail items with the stack support within the stack holder, the stack support arranged to be moved in a stacking direction and, coupled to the underfloor belt, aligning the mail items in an upright position on the stop wall, individually supplying and stacking the items of mail, one after another, by stacking belts of a covering belt system and a stacking roller, which is located at an entry to the stack holder and in the vicinity of the stop wall and protrudes from the stack wall, over which stacking roller one of the stacking belts is deflected, leading the items of mail at an acute angle in a longitudinal direction to the stack support on the latter or the last item of mail already stacked as far as the stop wall, controlling stacking pressure of the items of mail with a force measuring device for measuring the stacking pressure at the stacking point, the force measuring device connected to a device which is connected to the drive of the underfloor belt, for controlling the stacking pressure, the stacking pressure being measured directly on the stacking roller approximately perpendicular to the direction of the resultant belt force on the stacking roller, via a deflection of the stacking roller.
 2. The method according to claim 1, wherein the deflection of the stacking roller is transmitted to a bending beam having strain gages, whose deformation approximately perpendicular to a resultant force is used as a measure of the stacking pressure.
 3. The method according to claim 2, wherein the stacking roller can be deflected only approximately perpendicular to the direction of the resultant belt force.
 4. The method according to claim 2, wherein the force is transmitted from the deflectable stacking roller to the bending beam of the force measuring device by a connecting element, the connecting element being designed to be stiff in the force transmission direction approximately perpendicular to the resultant belt force and compliant at right angles thereto.
 5. The method according to claim 1, wherein the stacking pressure is measured only when there is as yet no following item of mail between stacking belt and a deflection roller for an other stacking belt, located upstream of the stacking roller in the transport direction.
 6. A device for stacking flat items of mail in an upright position, comprising: a stack holder for accommodating the mail at a stacking point, the stack holder comprising: an underfloor belt upon which the stack is positioned upright, the belt arranged to be moved in a stacking direction, a stop wall to which the stack is aligned; a stack support coupled to the underfloor belt; a stacking wall arranged parallel thereto at the stacking point, stacking belts of a covering belt system and a stacking roller located at an entry to the stack holder in the vicinity of the stop wall and protruding from the stack wall, and over which one of the stacking belts is deflected in order to supply and stack the items of mail so that the items of mail are led at an acute angle in a longitudinal direction to the stack support on the latter or the last item of mail already stacked as far as the stop wall, a force measuring device arranged to the stacking pressure at the stacking point, the measuring device being connected to a device which is connected to a drive of the underfloor belt, the measuring device further arranged to control the stacking pressure such that the stacking roller is mounted such that it can be deflected and the stacking roller mounting is connected by a connecting element to the force sensor belonging to the force measuring device in order to measure the stacking pressure perpendicular to the direction of the resultant belt force on the stacking roller.
 7. The device according to claim 6, wherein the force sensor provided in the force measuring device is a bending beam having strain gages, whose deflection approximately perpendicular to the resultant belt force on the stacking roller is arranged so as to be used as a measure of the stacking pressure.
 8. The device according to claim 6, wherein the stacking roller can be deflected only approximately perpendicular to the direction of the resultant belt force on the stacking roller.
 9. The device according to claim 7, wherein the mounting of the deflectable stacking roller is coupled by a connecting element to the bending beam of the force measuring device, the connecting element being designed to be stiff in the force transmission direction approximately perpendicular to the resultant belt force on the stacking roller and compliant at right angles thereto.
 10. The device according to claim 6, wherein the force measuring device is arranged to be adjustable.
 11. The device according to claim 6, wherein the stacking roller bearing is fixed to a movable swinging arm, which is connected to the connecting element. 